A hearing aid device may include a hearing aid housing, a microphone for converting sound into an audio input signal, and a signal processing unit adapted for processing the audio input signal into an audio output signal. A hearing aid may also include a sound emitter sized for being arranged in the ear canal of a human being. In some cases, the sound emitter (ear plug) may be arranged on one end of a conductor adapted for transmitting sound or electrical signal to the sound emitter.
Hearing aid devices of the above mentioned kind have been disclosed in US patent application publication nos. 2014079262 and no. 2009304216, and in U.S. Pat. No. 8,385,573.